^o ANGIOSPERMAE'-DICOTYLEDONES 



(Andrena gwynana K.), the brimstone butterfly (Rhodocera rhamni Z.), and a 

 Bombyliid (Bombylins medius Z., freq.). 



The following were recorded by the observers, and for the localities stated. 



Burkill (Yorkshire coast) ('Fertlsn. of Spring Fls.'). A. Coleoptera. i. An- 

 thobium (Eusphalerum) primulae Fauv. (=A. triviale Er), dvg. the anthers; 2. 

 Meligethes picipes Sturm., skg. B. Hymenoptera. Apidae : 3. Andrena gwynana 

 K. $, searching for nectar, but unable to reach it, C. Thysanoptera. 4. Thripn 

 sp., freq. Burkill elsewhere remarks that 'the fertilization of this plant is yet 

 unexplained. None of the insects seen on it through many hours of watching 

 are sufiicient for its fertilization.' Darwin, only Thrips: he says 'the primrose 

 is never visited (and I speak after many years' observation) by the larger humble- 

 bees and rarely by the smaller kinds.' Scott-Elliot (Dumfriesshire), the humble-bee 

 Bombus hortorum Z. Miller- Christy (Essex), 2 bees (Apis mellifica Z,, and 

 Anthophora acervorum Z.), humble-bees (Bombus sp.), a hover- fly (Syrphus sp.), 

 2 butterflies (Rhodocera rhamni Z., and Pieris rapi Z.), and a beetle (Meligethes 

 picipes Sturm.). Loew (Berlin Botanic Garden), the bee Anthophora pilipes F., 

 steadily skg. and po-cltg., and settling repeatedly. E. Bell (England) only noticed 

 4 visitors ' after seeing and examining thousands and thousands, we might say 

 millions of the flowers ' : he adds that ' the primrose gives unimpeachable evidence 

 that self-fertilization of heterostyled plants is the natural and legitimate fertilization as 

 being fully productive ' (' The Primrose and Darwinism '). F. E. Weiss (Shropshire), 

 the Bombyliid Bombylius major Z., freq. (also in North Staffordshire), the humble- 

 bee Bombus terrester Z., and 3 bees i. Andrena gwynana^., freq.; 2. Anthophora 

 pilipes F. ; 3. Apis mellifica Z. Miss M. L. Armitt (Westmoreland, teste Weiss), 

 Bombylius, eff"ecting crossing. Weiss endeavours to reconcile conflicting views: 

 ' The fact that many observers have been unable to detect such insect visitors 

 I attributed to their observations having been made either in cold or dull weather, 

 or in exposed and windy situations. For even on sunny days I could not observe 

 the usual insect visitors on primroses in wind-swept localities, while, at the same 

 time, in sheltered positions some larger humble-bees might occasionally be met 

 with on the primroses, and Anthophora, Bombylius, and pollen-gathering Andrenae 

 fairly regularly.' He'finally concludes : ' From the observations I have made on the 

 primrose, I feel convinced that it is both regularly visited and cross-pollinated by 

 insects under favourable climatic conditions, but that like most flowers adapted to the 

 visits of insects, it is provided with efficient means for self-poUination, and these are 

 important to a plant flowering at so early a period of the year when the visits of 

 insects may be precarious.' 



Ljungstrom graphically represents the relationship between the three species of 

 Primula just considered by means of a scalene triangle, of which the angles represent 

 the species, and in which the shortest side is between P. vulgaris and P. elatior, and 

 the longest between P. vulgaris and P. officinalis. 



P. elatior 



P. vulgaris ^^ -~- P. officinalis 



This diagram also indicates the degree of fertility of the hybrids, for the (pollen) 

 sterility of these increases as the affinity of the stocks crossed becomes more remote. 

 Ljungstrom examined the pollen of various hybrids and obtained the following 

 results. 



P. vulgaris x P. officinalis : 26-5-33 % normal pollen-grains, 73-5-67 % shrivelled 

 and useless. a 



I 



